<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    table {
      border: 1px solid #000;
      text-align: center;
      width: 300px;
    }
    th,td {
      border: 1px solid #000;
    }
    h3 {
      position: relative;
    }
    span {
      position: absolute;
      left: 145px;
      top: -4px;
      width: 16px;
      height: 16px;
      color: white;
      font-size: 12px;
      text-align: center;
      border-radius: 50%;
      background-color: #e63f32;
    }
  </style>
</head>
<body>

  <div id="app">
    <h3>小黑的礼物清单🛒</h3>
    <p>礼物总数-计算属性：{{total}}个</p>
    
    <table>
      <tr>
        <th>名字</th>
        <th>数量</th>
      </tr>
      <tr v-for="(item, index) in list" :key="item.id">
        <td>{{ item.name }}</td>
        <td>{{ item.num }}个</td>
      </tr>
    </table>

     <!-- 目标：统计求和，求得礼物总数 -->
    <p>礼物总数：{{ total }} 个</p>
    <p>礼物总数-计算属性：{{total}}个</p>
    <p>礼物总数-计算属性：{{total}}个</p>
    <p>礼物总数-计算属性：{{total}}个</p>
    <hr>
    <hr>
    <p>礼物总数-函数：{{totalFn()}}个</p>
    <p>礼物总数-函数：{{totalFn()}}个</p>
    <p>礼物总数-函数：{{totalFn()}}个</p>
    <p>礼物总数-函数：{{totalFn()}}个</p>
   
  </div>
  <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
  <script>
    const app = new Vue({
      el: '#app',
      data: {
        // 现有的数据
        list: [
          { id: 1, name: '篮球', num: 3 },
          { id: 2, name: '玩具', num: 2 },
          { id: 3, name: '铅笔', num: 5 },
        ]
      },
      // 方法
      methods:{
      totalFn(){
        console.log("❌methods方法多个地方调用，就会触发多次");
        const res = this.list.reduce((sum, item) => sum + item.num, 0)
        return res
      }
      },
        // 计算属性结构-性能更好-有缓存
      computed: {
        total() {
          console.log("🌈computed会缓存，可以在多个地方同时用");
          const res = this.list.reduce((sum, item) => sum + item.num, 0)
          return res
        }
      }
    })
  </script>
</body>
</html>